SCHG How-to:Correct Drowning Bugs in Sonic 1
From Sonic Retro
(Guide by redhotsonic)
These bugs are present in both Sonic's 1 & 2, but have been fixed in Sonic 3 (& Knuckles).
So, you're underwater, timer starts, can't find air, AND... you drown. But what happens if you get hurt as soon as you're about to drown? Watch this video and find out: 
Basically, what happens, is if you're hurt and you haven't landed yet, when you drown, Sonic will still be using the gravity from his falling back from hurt state. He will also be able to detect the floors and walls. Hence why in this video, I was able to move about after drowning. However, there is a timer present, and it will force you to the bottom of the screen and restart within seconds.
Also, in both 1 & 2, there is another bug, although, hard to pull off. If you drown around the 9:58 mark, then the timer hits 9:59 and you're still drowning, Sonic will all of a sudden zoom to the top of the screen then back down again, really fast, in his death animation. The Time over appears.
In Sonic 2, there is an extra bug. When you and Tails (sidekick) drowns (normally), when Sonic reaches to the bottom of the screen, if Tails hasn't yet, he will suddenly start flying and move closer to where you drowned, but will continue to fall downwards.
In Sonic 3 and Knuckles, all of these have been fixed. It doesn't matter if you're in the hurt state, Sonic will still fall normally and will ignore the floor. And unless Tails entered the water at the exact same time as you (like he does at the beginning of HCZ1), Tails will automatically start swimming to where you drowned but will not fall. If he did enter the water at the same time, he will drown with you, but won't have time to do that bug where he would start flying suddenly. Time over will still make an appearance if you drown near the 9:58 mark, but Sonic won't misbehave.
Now, I'm going to show you how to fix these bugs in Sonic 1 and Sonic 2, the way Sonic 3 and Knuckles did it. It's not that hard, I've done all the research for you. This guide will show you the fix for Sonic 1, for the SVN disassembly. If you are looking for the Sonic 2 fix, its here.
First, we need to make little edit to the drowning-routine. You need to open the "0A - Drowning Countdown.asm".
Go to "@reduceair:" and just after the "move.w #0,obInertia(a0)" command, insert this:
move.b #$A,obRoutine(a0) ; Force the character to drown
And just after "move.b #1,(f_nobgscroll).w", insert this:
move.b #0,(f_timecount).w ; Stop the timer immediately
So you have this:
@reduceair: subq.w #1,(v_air).w ; subtract 1 from air remaining bcc.w @gotomakenum ; if air is above 0, branch ; Sonic drowns here bsr.w ResumeMusic move.b #$81,(f_lockmulti).w ; lock controls sfx sfx_Drown ; play drowning sound move.b #$A,$34(a0) move.w #1,$36(a0) move.w #$78,$2C(a0) move.l a0,-(sp) lea (v_player).w,a0 bsr.w Sonic_ResetOnFloor move.b #$17,obAnim(a0) ; use Sonic's drowning animation bset #1,obStatus(a0) bset #7,obGfx(a0) move.w #0,obVelY(a0) move.w #0,obVelX(a0) move.w #0,obInertia(a0) move.b #$A,obRoutine(a0) ; Force the character to drown move.b #1,(f_nobgscroll).w move.b #0,(f_timecount).w ; Stop the timer immediately movea.l (sp)+,a0 rts
Next, go to "@loc_13F86:" and change all this:
@loc_13F86: subq.w #1,$2C(a0) bne.s @loc_13F94 move.b #6,(v_player+obRoutine).w rts ; =========================================================================== @loc_13F94: move.l a0,-(sp) lea (v_player).w,a0 jsr SpeedToPos addi.w #$10,obVelY(a0) movea.l (sp)+,a0 bra.s @nochange
@loc_13F86: subq.w #1,$2C(a0) bne.s @nochange ; Make it jump straight to this location move.b #6,(v_player+obRoutine).w rts
Right, that's the drowning-routine finished. Now, we need to make Sonic apply to this. Open the main ASM file and go to "Sonic_Index:" and add this line at the end of the table:
So you have:
Sonic_Index: dc.w Sonic_Main-Sonic_Index dc.w Sonic_Control-Sonic_Index dc.w Sonic_Hurt-Sonic_Index dc.w Sonic_Death-Sonic_Index dc.w Sonic_ResetLevel-Sonic_Index dc.w Sonic_Drowned-Sonic_Index
Next, find "include "_incObj\Sonic Loops.asm"" and just below it, insert this:
include "_incObj\Sonic Drowns.asm"
Then, in the "_incObj" folder, make a new ASM file called "Sonic Drowns.asm" and insert this:
; --------------------------------------------------------------------------- ; Sonic when he's drowning ; --------------------------------------------------------------------------- ; ||||||||||||||| S U B R O U T I N E ||||||||||||||||||||||||||||||||||||||| Sonic_Drowned: bsr.w SpeedToPos ; Make Sonic able to move addi.w #$10,y_vel(a0) ; Apply gravity bsr.w Sonic_RecordPosition ; Record position bsr.s Sonic_Animate ; Animate Sonic bsr.w Sonic_LoadGfx ; Load Sonic's DPLCs bra.w DisplaySprite ; And finally, display Sonic
There, all done. When you drown, everything will be normal. If you got hurt then drown, everything will still be normal and you won't be able to hit the floor, nor will you fall fast. Also, as soon as Sonic drowns, the timer will stop immediately, rather than continuing to countdown. Because of this, there is no way you can get Time Over when drowning.
BUT WAIT! There's just ONE MORE THING! You'll find that no bubbles come from Sonic's mouth when he is in his drowning animation. Bubbles come out of his mouth normally, and the countdown numbers work fine... but after he drowns, no bubbles come out. To fix this:
Go to label "loc_D362:" and between the label and it's first command, insert this:
cmpi.b #$A,(v_player+obRoutine).w ; Has Sonic drowned? beq.s loc_D348 ; If so, run objects a little longer
So you have this:
loc_D362: cmpi.b #$A,(v_player+obRoutine).w ; Has Sonic drowned? beq.s loc_D348 ; If so, run objects a little longer moveq #$1F,d7 bsr.s loc_D348 moveq #$5F,d7
Done. This allows objects to run for a little bit longer than normal, allowing the bubbles to run out of Sonic's mouth like normal.